Boiler

ABSTRACT

A boiler for use with oil or gas employs a two part cylindrical shell housing a combustion and primary heat recovery section mounted in one part and a bank of heat exchange tubes forming a secondary heat recovery section mounted in the other part. The combustion section consists of a completely immersed, large diameter firing tube in which combustion occurs and which constitutes the primary heat recovery section of the boiler. The bank of heat exchange tubes which carry the hot exhaust gases from the combustion chamber to the stack surround a closed end, tubular primary heat surface extender which extends into and is in substantial alignment with the firing tube.

United States Patent 1191 Olsen Feb. 26, 1974 BOILER Primary Examiner-Kenneth W. Sprague [76] lnvemor' 22 35: Park Attorney, Agent, or FirmEdmond T. Patnaude [22] F1led. June 14, 1972 ABSTRACT [21] Appl' 262782 A boiler for use with oil or gas employs a two part cy- 9 lindrical shell housing a combustion and primary heat [52] US. Cl. 122/52, 122/83, 122/90 recovery section mounted in one part and a bank of [51] Int. Cl. F22b 9/08 heat exchange tubes forming a secondary heat recov- [58] Field of Search 122/52, 72, 83, 84, 85, 90, ery section mounted in the other part. The combus- 122/93, 95, 135, 136 tion section consists of a completely immersed, large diameter firing tube in which combustion occurs and [56] References Cited which constitutes the primary heat recovery section of UNITED STATES PATENTS the boiler. The bank of heat exchange tubes which 3,392,711 7/1968 Wolfersperger 122/52 carry exhaust gases fmm the combustion 410,351 9/1889 Davidson 122/83 chamber the stack summd a closed tubular 192,165 6/1377 Hind v I 122/g3 primary heat surface extender which extends into and 866,77! 9/1907 Burns 122/93 is in substantial alignment with the firing tube.

863,829 8/1907 Andrews 122/72 1,488,359 3 1924 Lopez 122 52 9 Clam, 2 Drawing Flgul'es BOILER The present invention relates in general to hot water or steam boilers, and it relates more particularly to a new and improved construction which finds application in package type dual-fuel boilers.

BACKGROUND OF THE INVENTION Dualfuel boilers capable of burning either gas or oil are well-known in the art and in the case of horizontal boilers are generally of a type using a single, large diameter firing tube in which combustion takes place. The hot gases exiting the firing tube pass through one, two or three successive banks of smaller diameter heat exchange tubes which extend parallel to and surround the firing tube. Such boilers are costly to build, difficult to operate by unskilled operators, and expensive to maintain. lnherently, the prior art boiler designs require that the hot gases leaving the firing tube be deflected through 180 before passing through the first bank of heat recovery tubes. Similar reversals of the hot gases are required for each successive bank of tubes, and the use of refractory brick is commonly used for this purpose in spite of the expense required to maintain it in operative condition. The use of water backed end plates for reversing the flow of hot gases is also used but is substantially more costly.

Another disadvantage inherent in the prior art boilers has been the unequal stresses exerted on the tube sheets by the firing tube and the several banks of heat exchange tubes due to unequal expansion and contraction of the tubes resulting from the different temperatures at which they operate. This is a common cause of tube leakage which has plagued the industry since the advent of forced circulation between the boiler and the associated radiation.

Still another disadvantage of the prior art boilers of this general type has been the need to use relatively small diameter firing tubes. While it is well recognized that combustion is impaired when the firing tube diameter is reduced, in order to provide acceptable gas discharge temperatures at the stack or chimney, a large number of heat recovery tubes are necessary which thus restricts the diameter of the firing tube for a given size boiler shell.

OBJECTS OF THE INVENTION Therefore, an object of the present invention is to provide a new and improved boiler design which eliminates reversals in the direction of gas flow there through between the combustion chamber and the hot gas outlet.

Another object of this invention is to provide a new and improved boiler using heat recovery tubes in a manner avoiding any substantial nonuniform stresses on the tube sheets between which the tubes .are mounted.

A further object of this invention is to provide a new and improved boiler employing novel means for recovering heat from the combustion section.

A still further object of this invention is to provide a novel package type boiler which may be manufactured, transported and installed at a lower cost then those of the prior art.

SUMMARY OF THE INVENTION I Briefly, the above and further objects may be realized in accordance with the present invention by providing a boiler shell housing a combustion and primary heat recovery section in one part and a secondary heat recovery section in another part, which parts are in axial alignment. The boiler shell is made in two parts with the firing tube mounted in one part and the secondary heat recovery tubes mounted in the other part. A closed end, tubular heat surface extender is mounted by the inner tube sheet of the secondary heat recovery section and extends into the downstream end of the firing tube to provide a substantially greater primary heat exchange surface thereby reducing the number of heat exchange tubes required in the secondary heat recovery section. In addition, the extender provides better distribution of the hot gases from the firing tube to the secondary heat recovery tubes.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects and advantages and a better understanding of the invention may be had from the following detailed description taken in connection with the accompanying drawings, wherein:

FIG. 1 is an elevational view, partially broken away and sectioned, of a hot water boiler embodying the present invention; and

FIG. 2 is a sectional view taken along the line 2-2 of FIG. I particularly showing the tube arrangement in the secondary heat recovery section.

DETAILED DESCRIPTION OF THE DRAWINGS Referring now to the drawings and particularly to FIG. 1 thereof, a hot water boiler 10 includes a generally tubular shell 11 formed in two parts, 11a and 11b, connected together by a plurality of arcuate plates forming a ring 12 which is suitably bolted, riveted or welded to the shell sections 11a and 11b. As is more fully described hereinafter, the shell section 1 1a houses and provides the sole support for the combustion and primary heat recovery section of the boiler and the shell section 11b houses and provides the sole support for the secondary heat recovery section of the boiler.

The front end of the shell section 11a is closed by a circular end plate 13 secured in the end of the shell by suitable welding. A firing tube 14 in which the combustion chamber 15 is located extends through a circular opening 16 in the front plate 13 and is secured thereto as by welding. The rearward end of the firing tube 14 is supported by a rear plate assembly including a circular plate 17 provided with a circular opening 18 for receiving the firing tube 14. The plate 17 is welded to a tubular section 19 which is in turn welded to a ring 20. The plate 17, the tube 19 and the ring 20 are thus welded together to form a unitary assembly with the ring 20 being welded to the shell 11a. Accordingly, the firing tube 14 is mounted in the shell section 11a completely independently of the shell section 11b. The tube 19 defines with the opposite portion of the shell section 11a an annular water leg for insulating the shell from the hot gases exiting the firing tube 14.

An insulator 23 formed of a heat refractory is fitted in the front end of the firing tube 14 which is provided with a forward flange 48 to facilitate mounting of the insulator 23 and to prevent movement thereof into the combustion chamber 15.

The boiler 10 is suitable for use with either a gas burner or an oil burner. As illustrated in FIG. 1 an oil burner 24 is provided for directing the ignited fuel through the opening in the refractory ring 23 into the combustion chamber 15. Inasmuch as the burner 24 is of any suitable conventional construction and is not a part of the present invention, it is not described in detail herein.

Mounted in the shell section 1 lb are a pair of circular tube sheets 26 and 27 between which a plurality of heat exchange tubes 28 are mounted. Preferably, the sheets 26 and 27 are provided with mutually aligned, drilled holes in which the ends of the tubes 28 are respectively positioned and rolled in place to seal the peripheries of the tubes 28 to the respective sheets 26 and 27. The arrangement of the tubes 28 is best illustrated in FIG. 2 but is not critical. A rear end plate 29 is secured as by welding over the rear end of the shell section 11b in spaced apart relationship from the rear tube sheet 27 to provide a cylindrical chamber 30 through which the hot gases exiting the tubes 28 pass to a gas outlet 31 and from there to the stack or chimney. A pressure relief door assembly 32 is mounted over an opening in the rear plate 29 to protect against explosion hazards and accidental pufi back damage arising from a control failure or other cause. During normal operation the door assembly 32 is closed and the hot gases are exhausted from the boiler through the outlet 31 at the top.

In order to enable an efficient, straight through boiler design of practial size, there is provided in accordance with an important feature of the present invention a heating surface extender 33 which is mounted solely by the tube sheet 26 and extends a substantial distance into the combustion chamber 15 within the firing tube 14. The heating surface extender 33 comprises a tube 34 closed by a generally circular end member 35 which may be planar or dished as illustrated in the drawings.

A water inlet duct 36 extends through the shell section 11b into the bottom of the chamber in the secondary heat recovery section between the tube sheets 26 and 27, and in a conventional heating installation is connected to the return line from the radiation. The water in the secondary heat recovery section is circulated to the chamber within the primary heat recovery section by means of a circulating duct 38 interconnected between the two sections near the top of the boiler and by a pump 39 connected in a duct 40 which extends between the boiler sections at the bottom. It will be understood by those skilled in the art that the circulating duct 38 must be located below normal water level in the boiler and in a steam boiler it will necessarily be lower than illustrated in the drawings. Similarly, the upper ones of the heat recovery tubes 28 shown in the drawings would necessarily be eliminated in a steam boiler since all of the tubes 28 must also be below water level. As illustrated schematically, the

- pump 39 pumps water from the bottom of the secondary heat recovery section in the shell part 11b to the primary heat recovery chamber in the shell part 11a. A hot water or steam outlet 41 is provided at the top of the boiler near the front thereof and is connected in a normal heating installation to the inlet side of the radiation.

The boiler 10 may be manufactured in two parts, the combustion section which is entirely mounted by the shell section 11a being manufactured as one part and the secondary heat recovery section being independently mounted by the rear shell section 11b as a separate part. These two parts may be transported separately to the site of use and there assembled in in-line relationship with a ring of heat refractory material 43 positioned between the ring 20 and the tube sheet 26, as illustrated in FIG. 1. The burner 24 or other suitable burner such as a gas burner is then installed at the front of the boiler, the outlet 31 is connected to the chimney and the inlet 36 and the outlet 41 are connected to the heating system. When the boiler shell is filled with water it may be seen that the tubes 28 are immersed in water and the heat extender 33, being below water level, is filled with water. With the pump 31 operating, the water chamber in the shell section 1 1a surrounding the firing tube is also filled with water. When the burner is fired, all of the combustion takes place in the combustion chamber 15 and the wall of the firing tube 14 conducts a major portion of the heat generated in the chamber 15 to the water in the shell section 11a. The extremely hot gases in the firing tube also impinge directly on the end of the heat surface extender 23 to heat the water contained therein which, of course, is constantly circulating. The hot, burned gases exiting the rear end of the firing tube 14 pass through the annular area surrounding the heat surface extender and then pass to the secondary heat recovery tubes 28 through the annular manifold area defined between the plate 17, the tube 19 and the tube sheet 26. As these hot gases pass through the tubes 28 into the chamber 30 from which they exit the boiler through the outlet 31, heat is transferred through the tube walls to the water in the shell section 11!). Since the required total area of the tubes 28 necessarily exceeds the crosssectional area of the combustion chamber 15, the heat surface extender 33, in addition to providing a large primary heat transfer surface, functions as a baffle or distributor to provide substantially uniform distribution of the hot gases to the tubes 28. It is apparent that in the absence of the heat extender, the in-line relationship of the firing tube 14 with the tubes 28 would cause short circuiting or bypass of those tubes not directly aligned with the combustion chamber 15.

It may seem that the boiler construction of the present invention provides uniform stresses on the tube sheets 26 and 27 inasmuch as all of the tubes 28 are op.- erated at substantially the same temperature. This is in contrast to the prior art type of horizontal boiler wherein several banks of secondary heat recovery tubes are arranged in concentric rings around the central firing tube. Similarly, the firing tube 14 is supported independently of the tube sheets 26 and 27 wherein the expansion and contraction of the firing tube 14 does not exert any force on the tube sheets 26 and 27. Again, this is in contrast to the prior art boiler constructions wherein the centrally disposed firingtube is commonly mounted by the same tube sheets in which the several banks of secondary heat recovery tubes are mounted. If desired, a baffle or a plurality of helically disposed bafi'les can be mounted on the external surface of the heat extender tube 34 to provide better distribution of the hot gases to the tubes 28 and across the cylindrical surface of the heat extender for better heat transfer. Under normal operating conditions, however,

the appended claims are intended to cover all such changes and modifications as fall within the true spirit and scope of the present invention.

What is claimed is:

l. A boiler, comprising an elongated shell housing a combustion section constituting a primary heat recovery zone and a secondary heat recovery section,

said sections being in mutual in-line relationship,

said combustion section including a firing tube mounted in spaced apart relationship with the sides of said shell to provide an annular chamber surrounding said tube,

an exhaust outlet at the end of said secondary heat recovery section, I

said secondary heat recovery section ihcluding a plurality of heat exchange tubes interposed in substantial parallel relationship between said firing tube and said exhaust outlet for carrying the hot gases to said outlet and extracting heat therefrom,

inlet means for supplying water to said shell to maintain said firing tube and said heat exchange tubes immersed in water,

outlet means connected to the upper portion of said shell, and

a generally tubular heat surface extender protruding into said firing tube from said secondary heat recovery section with the distal end of said extender being closed and with the interior thereof opening onto the space surrounding said heat exchange tubes, thereby to be filled with water.

2. A boiler according to claim 1 wherein is provided a tube sheet mounted in said shell between said combustion section and said secondary heat recovery section, and wherein said sheet is provided with one opening over which said extender is mounted and a plurality of other openings disposed around said one opening and in which said heat exchange tubes are mounted, one side of said sheet being in communication with the chamber in said firing tube to' provide additional heat transfer surface area.

3. A boiler according to claim 2 wherein said shell is formed of two separate and interconnected parts,

one of said parts housing said combustion section,

and

the other of said parts housing said secondary heat recovery section.

4. A boiler, comprising an elongated shell housing a combustion section constituting a primary heat recovery zone and a secondary heat recovery section,

said sections being in mutual in-line relationship,

said combustion section including a firing tube mounted in spaced apart relationship with the sides of said shell to provide an annular chamber surrounding said tube,

an exhaust outlet at the end of said secondary heat recovery section,

said secondary heat recovery section including a plurality of heat exchange tubes interposed in substantial parallel relationship between said firing tube and said exhaust outlet for carrying the hot gases to said outlet and extracting heat therefrom,

inlet means for supplying water to said shell to maintain said firing tube and said heat exchange tubes immersed in water,

outlet means connected to the upper portion of said shell, and said shell is formed of two separate and interconnected parts, one of said parts housing said combustion section, and the other of said parts housing said secondary heat recovery section.

5. A boiler according to claim 4 comprising pump means for circulating water between said combustion section and said secondary heat recovery section,

said inlet means opening into said secondary heat recovery section, and

said outlet means opening into said combustion section.

6. A boiler, comprising an elongated shell housing a combustion section constituting a primary heat recovery zone and a secondary heat recovery section,

said sections being in mutual in-line relationship,

said combustion section including a firing tube mounted in spaced apart relationship with the sides of said shell to provide an annular chamber surrounding said tube,

an exhaust outlet at the end of said secondary heat recovery section,

said secondary heat recovery section including a plurality of heat exchange tubes interposed in substantial parallel relationship between said firing tube and said exhaust outlet for carrying the hot gases to said outlet and extracting heat therefrom,

inlet means for supplying water to said shell to maintain said firing tube and said heat exchange tubes immersed in water,

outlet means connected to the upper portion of said shell,

a tube sheet mounted in said shell and provided with a plurality of holes receiving said heat exchange tubes,

means mounting said firing tube including a generally annular plate coplanar with said tube sheet connected between said shell and the distal inner end of said firing tube, and

heat insulation interposed between opposing face portions of said plate and said sheet.

7. A boiler according to claim 6 wherein said shell comprises two separate parts connected together between said plate and said tube sheet.

8. A boiler comprising an elongated, hollow, cylindrical shell supported in a horizontal position,

a combustion and primary heat recovery section mounted in the front portion of said shell and a secondary heat recovery section mounted in the rear portion of said shellin mutual alignment with said combustion and primary heat recovery section,

a hot gas exhaust outlet mounted at the rear of said 55 shell in communication with said secondary heat recovery section, and

means for circulating water between said sections.

9. A boiler of the type including a combustion chamber and a plurality of secondary heat recovery tubes through which the hot gases from said chamber are passed, said chamber and said tubes being immersed in water during operation of said boiler, the improvement comprising a primary heat surface-extender positioned directly within said combustion chamber,

said extender being substantially hollow with the cavity therein in communication with the water in said boiler. 

1. A boiler, comprising an elongated shell housing a combustion section constituting a primary heat recovery zone and a secondary heat recovery section, said sections being in mutual in-line relationship, said combustion section including a firing tube mounted in spaced apart relationship with the sides of said shell to provide an annular chamber surrounding said tube, an exhaust outlet at the end of said secondary heat recovery section, said secondary heat recovery section ihcluding a plurality of heat exchange tubes interposed in substantial parallel relationship between said firing tube and said exhaust outlet for carrying the hot gases to said outlet and extracting heat therefrom, inlet means for supplying water to said shell to maintain said firing tube and said heat exchange tubes immersed in water, outlet means connected to the upper portion of said shell, and a generally tubular heat surface extender protruding into said firing tube from said secondary heat recovery section with the distal end of said extender being closed and with the interior thereof opening onto the space surrounding said heat exchange tubes, thereby to be filled with water.
 2. A boiler according to claim 1 wherein is provided a tube sheet mounted in said shell between said combustion section and said secondary heat recovery section, and wherein said sheet is provided with one opening over which said extender is mounted and a plurality of other openings disposed around said one opening and in which said heat exchange tubes are mounted, one side of said sheet being in communication with the chamber in said firing tube to provide additional heat transfer surface area.
 3. A boiler according to claim 2 wherein said shell is formed of two separate and interconnected parts, one of said parts housing said combustion section, and the other of said parts housing said secondary heat recovery section.
 4. A boiler, comprising an elongated shell housing a combustion section constituting a primary heat recovery zone and a secondary heat recovery section, said sections being in mutual in-line relationship, said combustion section including a firing tube mounted in spaced apart relationship with the sides of said shell to provide an annular chamber surrounding said tube, an exhaust outlet at the end of said secondary heat recovery section, said secondary heat recovery section including a plurality of heat exchange tubes interposed in substantial parallel relationship between said firing tube and said exhaust outlet for carrying the hot gases to said outlet and extracting heat therefrom, inlet means for supplying water to said shell to maintain said firing tube and said heat exchange tubes immersed in water, outlet means connected to the upper portion of said shell, and said shell is formed of two separate and interconnected parts, one of said parts housing said combustion section, and the other of said parts housing said secondary heat recovery section.
 5. A boiler according to claim 4 comprising pump means for circulating water between said combustion section and said secondary heat recovery section, said inlet means opening into said secondary heat recovery section, and said outlet means opening into said combustion section.
 6. A boiler, comprising an elongated shell housing a combustion section constituting a primary heat recovery zone and a secondary heat recovery section, said sections being in mutual in-line relationship, said combustion section including a firing tube mounted in spaced apart relationship with the sides of said shell to provide an annular chamber surrounding said tube, an exhaust outlet at the end of said secondary heat recovery section, said secondary heat recovery section including a plurality of heat exchange tubes interposed in substantial parallel relationship between said firing tube and said exhaust outlet for carrying the hot gases to said outlet and extracting heat therefrom, inlet means for supplying water to said shell to maintain said firing tube and said heat exchange tubes immersed in water, outlet means connected to the upper portion of said shell, a tube sheet mounted in said shell and provided with a plurality of holes receiving said heat exchange tubes, means mounting said firing tube including a generally annular plate coplanar with said tube sheet connected between said shell and the distal inner end of said firing tube, and heat insulation interposed between opposing face portions of said plate and said sheet.
 7. A boiler according to claim 6 wherein said shell comprises two separate parts connected together between said plate and said tube sheet.
 8. A boiler comprising an elongated, hollow, cylindrical shell supported in a horizontal position, a combustion and primary heat recovery section mounted in the front porTion of said shell and a secondary heat recovery section mounted in the rear portion of said shell in mutual alignment with said combustion and primary heat recovery section, a hot gas exhaust outlet mounted at the rear of said shell in communication with said secondary heat recovery section, and means for circulating water between said sections.
 9. A boiler of the type including a combustion chamber and a plurality of secondary heat recovery tubes through which the hot gases from said chamber are passed, said chamber and said tubes being immersed in water during operation of said boiler, the improvement comprising a primary heat surface-extender positioned directly within said combustion chamber, said extender being substantially hollow with the cavity therein in communication with the water in said boiler. 